This application is related to copending application Ser. No. 272,129 pending for "Monolithic Series-Connected Solar Cells Employing Shorted P-N Junctions For Electrical Isolation" and to copending application Serial No. 272130 pending for "Method of Fabricating Back Surface Point Contact Solar Cells."
This invention relates generally to silicon solar cells having interdigitated back contacts, and more particularly the invention relates to such solar cells having internal bypass diodes.
The silicon solar cell comprises a plurality of p and n conductivity type regions in a silicon body which generate a voltage potential and/or a current when electron-hole pairs are created in the semiconductor body in response to impinging radiation, and the holes and electrons migrate to the p-doped regions and the n-doped regions, respectively. In a solar cell having interdigitated back surface contacts, the p and n regions are formed in alternating rows with a metal contact provided for contacting all of the doped regions in one row and with all rows of like dopant regions being connected in parallel.
It is recognized that partial shading of solar cell modules can cause a disproportionate loss in module output or local overheating and module destruction. See Green et al., "Silicon Solar Cells with Integral Bypass Diodes," Conference Record, 17th IEEE Photovoltaic Special Conference, May 1-4, 1984. A shaded cell causes a drop in module current, and the drop in current increases the operating voltage of the unshaded cells. The extra voltage generated drives down the voltage across the shaded cell in an attempt to increase the current through it. With even small amounts of shading, the shaded cell will become reverse-biased and become a dissipator of electrical power. One technique used to overcome the problem is the provision of bypass diodes connected across groups of cells. This limits the power dissipation in the shaded cell to the maximum generating capacity of the remainder of the cells in a group.
Green et al. propose a silicon solar cell structure with integral bypass diodes incorporated in the cell structure. The main cell comprises a p-n junction formed by an n region in one surface of a p-type substrate. The bypass diode comprises an n region in the opposing surface of the p-type substrate and laterally displaced from the main cell. The semiconductor body portion between the main cell and the bypass diode provides electrical isolation between the cell and the diode. The technique does require an additional processing step, and the resistance of the semiconductor body provides limited isolation unless treated to increase the resistance thereof.